The invention relates to a method and apparatus for determining potential shifts between electronic modules in a wire bus network or the correspondence quality of their communications operating levels in the network interconnection.
Control technologies which rely on a simple wire bus as a communications medium are becoming increasingly important. Examples thereof that have been disclosed are bus networks according to the J1850 or CAN standard which a rely on a two-wire bus medium. In this case, a multiplicity of electronic control units communicate with one another via two conductor cores which are normally dominantly keyed in antiphase.
In this context, WO 90/08437 describes the coupling of a subscriber of a local network, in particular of a motor vehicle, which has at least one transmitting and/or one receiving section to a data bus of this type having two bus lines. This coupling is designed in such a way that the potentials which occur at the input terminals of a subscriber are used to enable reliable identification of the data present on the data bus. The identification is possible even in the event of a short circuit of one of the bus lines with respect to earth ground, the battery voltage or with respect to the other bus line, or in the event of one of the bus lines being interrupted.
WO 90/09713 describes a network interface of a computer network, in particular for a motor vehicle, which has at least two bus lines. Here, the network is distinguished by an error detection circuit which is assigned to the bus lines and to a reference voltage and, in the event of an interruption, or a short circuit of one of the two bus lines to earth or a supply voltage of the computer network, the error detection circuit evaluates a signal arriving on the other, intact bus line and outputs a wake-up signal for the purpose of activating the network interface.
German Patent Document DE 42 27 035 A1 describes an arrangement for bidirectional data transmission on a two-wire bus system which functions in the single-wire operating mode if a large number of line faults occur. At the same time, the arrangement prevents power losses even in the event of a short circuit of a data line to a high battery voltage.
German Patent Document DE 43 42 036 C1 describes a data bus system which has a serial data bus that is operated by complementary logic signals. The system also has a plurality of subscribers which communicate with one another via the bus lines. Each bus line has bus-coupling output stages. Part of the output stage of each bus subscriber is a bus termination network. Here, the bus termination network is designed such that it has a low impedance and is active. Furthermore, the termination network is designed such that it is switchable and at least one output stage can be changed over internally. On the other hand, the bus termination network is designed such that it is passive and at least one further output stage has a low impedance. Further, the bus termination network is designed such that all the remaining output stages have a high impedance.
Bus networks have also been disclosed which utilize, as the bus medium, a single line core over a busbar or collective surface that also serves (as a rule) as a power supply conductor. Communication is effected in each case by transmitting/receiving means - so-called bus transceivers. As an essential part of each device, these bus transceivers are each physically coupled to the bus medium. These transceivers for transmitting and receiving the data messages convert the latter from the logic level within the relevant bus subscriber into signal levels on the bus core or cores, and vice versa.
With regard to various features of a suitable bus transceiver which are relevant in the context of the present invention, reference is expressly made to DE 196 11 944 A1, the text of which is incorporated herein in its entirety.
Without exception, the bus subscribers perform their task (for example, control) via a micro-controller having a varying degree of performance. A protocol function is provided for communication via the bus. The protocol function may be previously monolithically cointegrated in microcontrollers which are specialized for such applications.
In the interest of a high signal-to-noise ratio, two-wire bus media are preferably used in systems in interference-critical surroundings, since single-wire bus media over a reference conductor surface are more sensitive to electromagnetic interference irradiation and radiation. This means that they can only be used at a low data rate. On the other hand, with a suitable configuration of their transceivers, two-wire bus networks can also be operated (in an emergency) in the aforementioned single-wire operating mode if appropriate at a lower data rate (i.e. one bus core with respect to a reference level that is available throughout the network).
In such networks, normal communication is predominantly effected by in-antiphase keying of the two line core potentials from a recessive to a dominant signal level. As a result of this measure and as a result of relatively low signal levels overall (seen in absolute terms), the interference radiation of corresponding bus networks can be kept relatively low. This is true even in the case when they are provided without screening and are operated with very short bus bit times.
The capability of using an unscreened two-core line as the bus medium is a precondition in many applications, both in terms of cost-effectiveness and adequate system availability under harsh operating conditions. The latter is easily understood when considering that transmission interference can actually occur in a screened bus system if the screening network has a fault, i.e., when a fault indication is not actually present on the bus cores serving for signal transmission and the network interconnection thereof. This fault possibility is necessarily absent from a two-wire bus system that is not based on screening. Additionally, in single-wire networks, communication is effected (as a rule) by keying the bus cores from a recessive to a dominant signal level with respect to the reference conductor surface. The invention can be used equally with single-wire and two-wire bus networks.
In both single-wire and two-wire bus systems, it is necessary to provide particular circuit conditions to keep the above-mentioned signal levels within certain tolerance windows so that interference-free signal transmission is possible between the bus transceivers.
In this respect, both the microcontroller and the bus protocol function require an operating voltage which is to be kept within narrow limits. As a rule, this operating voltage is derived from a superordinate potential via a voltage regulator contained in the control unit. In the case of transmission, the (one of the two) source level, which is dominant during transmission, is then determined from this relatively accurate operating voltage, by which source level data is xe2x80x9cgatedxe2x80x9d from the (respective) bus core at a recessive level.
For example, in a two-wire bus network according to the CAN standard, the dominant high level of 5 volts, which is specified at the present time, is derived from the supply voltage of 5 volts. Use of a 5 volt supply has long been customary for integrated circuit functions in control units. Here, the voltage can (in any case) be kept relatively and accurately constant in each unit using electronic regulating means.
The transceivers are designed in such a way that they implement the corresponding level conversions of the data messages without any errors even when the reference levels of the transceivers have, with respect to one another, certain mutual permissible potential differences. Here, these differences do not exceed a maximum value in each case.
Transmission problems inevitably arise in the above-mentioned single-wire or two-wire bus network. This occurs when the correspondence (within specified tolerance bands) of the bus level(s) dominantly established in terms of transmission on the bus core/cores and/or of the effective discrimination level(s) (coordinated therewith in terms of reception) for assessing the truth of signal edges and states in the bus medium suffers, or is impaired to an extent such that the above-mentioned maximum values are exceeded. In this respect, a sufficient correspondence of the levels at the same time appears to be an essential measure of a definable bus quality. This also incorporates other aspects such as, for example, the edge-rise correspondence between transmitter and receiver (slew rate compliance), the measure of overshoot attenuation, etc.
A specific case of the above-mentioned bus level disturbances are potential disturbances which are subscriber-induced locally. Such disturbances occur when a supply potential of all the bus subscribers is drawn from a common ( i.e., spatially extended) busbar or power service. Within the latter, an erroneous voltage drop occurs, with the result that the affected supply potential (as seen from the bus medium) is no longer the same for all the bus subscribers.
In the exemplary case of a control unit in a means of transport, in which the entire body serves (in a known manner) as a distribution conductor surface (xe2x80x9cearthxe2x80x9d), this occurrence may be due to an erroneous longitudinal voltage drop in this surface or an erroneous earth connection of a control unit as bus subscriber. Here, with application of the normal earth current of the relevant unit, an excessively large voltage drop and, in this respect, an increase in the earth reference potential of the affected unit with respect to the earth potentials of the remaining units in the bus network occurs. Consequently, such a control unit cannot then even be addressed any longer via the bus. This is because as a result of the earth-reference-point error voltage, the discrimination level window of its bus receiver, which is error-free per se, may be raised too far relative to others. For practical servicing and corrective maintenance of corresponding bus networks, it is very important to be able to identify the presence of corresponding potential shifts and to be able to determine the latter.
An object of the invention, therefore, is to provide a method and apparatus for determining potential shifts between electronic modules in a wire bus network or the correspondence quality of their communications operating levels in the network interconnection.
This object is achieved by the method according to the invention where at least one bus subscriber (test subscriber), which may be a subscriber that is normally connected to the bus or a subscriber that is only temporarily connected to the bus (such as, for example, a test unit in the workshop) and at the transmitting end a voltage offsetxe2x80x94designated as offset voltage in the following textxe2x80x94is added to (at least) one (of the two) dominant, normal source level and a test message is transmitted into the bus network by the test subscriber in this state. In this case, the source level is altered in a predetermined manner.
Depending on whether the (at least) one (of the two) dominant source level is decreased or increased by the offset voltage that can be set in each case, the (reference-earth-) potential-defective bus subscriber loses or gains its reception capability.
In the event of step-by-step monotonic alteration of the offset voltage, the (reference-earth-) potential-defective bus subscriber, in the first case, can no longer (correctly) receive the test message. Consequently, the potential bus subscriber also can no longer acknowledge the offset voltage as error-free and as the first of all the bus subscribers. In the second case, the potential bus subscriber can (correctly) receive and acknowledge it as the first of all the bus subscribers. The remaining bus subscribers are in this case put into or held in a status of no transmission capability (RECEIVE ONLY).
In order to localize that bus subscriber in which the largest reference-earth-potential-distorting error voltage throughout the bus network is effective, according to the method of the present invention a dominant H potential, for example, is thus reduced in a (stimulating) bus subscriber. This proceeds from a higher value, until one of the bus subscribers can no longer receive the (stimulating) test subscriber. The bus subscriber which loses its reception capability is then that bus subscriber which currently has the largest reference voltage error in the network. Or, for example, at least one dominant L potential is reduced, proceeding from an increased value compared with its normal value, until a bus subscriber can receive the (stimulating) bus subscriber. This subscriber which acquires reception capability is then actually that subscriber which has the largest reference voltage error in the network.
As a result of this measure according to the method of the present invention, it is thus possible to find not only the error-voltage-impaired bus subscriber but also, from the offset voltage reached in the case of the disappearing or incipient reception capability of the said bus subscriber, a measure of the size of the reference voltage error present in this bus subscriber.
According to another object of the invention, an apparatus is provided which is suitable for determining potential shifts between electronic modules in a wire bus network or the correspondence quality of their communications operating levels in the network interconnection. In this case, the bus medium comprises at least one wire and the electronic modules are directly electrically connected to the bus medium and furthermore are interconnected via a potential busbar. Here, the busbar serves as a reference-earth potential busbar for the bus communication in the case of the single-wire operating mode of the bus medium. Further, each electronic module comprises a micro-processor or micro-controller and also means for realizing transmission and reception coupling of the microprocessor or microcontroller to the bus medium.
According to the invention, the apparatus comprises, as part of the transceiver means, means for inhibiting the transmitting means during reception and also cooperative potential control means. These are connected to the microprocessor or microcontroller and are connected or can be connected to the transceiver means. Using these, with regard to parts of the transmitting and/or receiving means of the transceiver means, the apparatus numerically realizes at least one controllable voltage source. This numerically allows the influence of at least one source level which is dominant during transmission and/or at least one signal level which is discriminant during reception.
In an embodiment according to the invention, the potential control means can be driven digitally by a microprocessor or microcontroller.
In still another embodiment according to the invention, the potential control means are configured in such a way that in the event of transmission, at least one source level, which determines the dominant state on the relevant bus wire, can be shifted monotonically at least incrementally and/or decrementally.
In yet another embodiment of the present invention, the context of the capability of influencing two source levels which are dominant during transmission, can be both set or altered independently of one another.
In a further embodiment according to the invention, two source levels which are dominant during transmission can be set or shifted in such a way that the interval separating both levels is essentially maintained in the process.
In even a further embodiment according to the invention, the apparatus has a signal-dedicated terminal as reference-earth potential busbar at least the receiving means of the transceiver function.
In still another embodiment of the present invention, the apparatus comprises a particular terminal as reference-earth potential busbar at least of the means for setting or alteration in the event of transmission of at least of one of the two dominant source levels.
In another embodiment of the present invention, the apparatus has a particular terminal, via which the potential control means can be operatively connected to a reference-earth potential in the environment of the electronic module carrying the transceiver function.
In still another embodiment of the present invention, the apparatus comprises, in the path of the operative connection, means for protection against over voltage and/or an incorrect polarity and/or inputting a radio-frequency signal.
In yet another embodiment in the present invention, the apparatus acquires an adjustable offset voltage source, which is fed to the supply terminal of the transmitting means that is near to the reference-earth potential, and supplies the transmitting means with a constant voltage.
In a further embodiment of the present invention, at least parts of analog action of the receiving means are connected in parallel with the constant-voltage-supplied transmitting means in terms of power supplying, and the offset voltage source is thus also effective at the receiving end.
In another embodiment according to the invention, the apparatus acquires a first adjustable offset voltage source, which is fed to the supply terminal (near to the reference-earth potential) of the switching output stage of the transmitting means which drives the bus wire BUS_L. Along with this, a second adjustable offset voltage source is fed into a supply terminal, which has an opposite potential to the switching output stage of the transmitting means which drives the bus wire BUS_H.
In still another embodiment of the present invention, the apparatus acquires a first adjustable offset voltage source, which is fed to the supply terminal (near to the reference-earth potential) of the switching output stage of the transmitting means which drives the bus wire BUS_L. Also, a second and third adjustable offset voltage source, are fed into a supply terminal, which has an opposite potential to the switching output stage of the transmitting means which drives the bus wire BUS_H. Here, the latter voltage sources are referenced to supply potentials of different magnitudes or are connected to supply potentials of different magnitudes.
In yet a further embodiment of the present invention, the second and third offset voltage sources can be activated alternatively.
In still a further embodiment according to the invention, the offset voltage source (QSL) is referenced to the reference-earth potential, and the effective offset voltage source (remote from the reference-earth potential) can be only activated alternately in chronological succession.
In accordance with a further embodiment of the present invention, the apparatus comprises means which permit activation of the second and third offset voltage sources in a manner which is dependent upon the transmission signal.
In accordance with still a further embodiment of the present invention, the potential control means comprise means for autonomous alteration of the setting of at least one offset voltage source over time.
In accordance with a further embodiment of the invention an autonomous, alteration is possible in a manner which is dependent upon the data signal at the transmitting end.
In yet another embodiment of the present invention, a clock signal, which can be obtained from the microprocessor or microcontroller, can be fed to the means for autonomous alteration of the setting of at least one offset voltage source.
In still another embodiment of the invention, the potential control means comprise regulating means which permit the potential control to be performed in accordance with a value specification. This value specification can be received from the microprocessor or microcontroller, in a manner which is dependent upon a potential that can be obtained by tapping a bus wire.
In a further embodiment of the invention, the apparatus comprises (independently of the transmitting means) backup means which are connected or can be connected to at least one bus wire. The backup means also permit connection (keyed by the transmission signal) to the at least one bus wire of a regulated potential.
In another embodiment according to the invention, the apparatus comprises measuring means, which afford the acquisition of an error quantity (caused by the backup means) for the purpose of its compensation by regulating a connection or computational allowance in the desired value specification for the regulation performed by the microprocessor or microcontroller.
In accordance with another embodiment of the invention, the apparatus comprises (independently of the transmitting means) backup means which are connected or can be connected to at least one bus wire. With the backup means, a connection which is keyed by the transmission signal is possible to the bus wire of an unregulated potential in accordance with a digital value which can be predetermined by the microprocessor or microcontroller.
In still a further embodiment, for the purpose of activating one of the backup means, the backup means can receive the transmission signal from the relevant core output stage via a changeover switch. If appropriate, the changeover switch disconnects the output stage from the bus wire.
In accordance with another embodiment of the invention, the regulating means comprise a sampler, which is operatively connected to a bus wire, and a holding element or a holding regulator.
In an even further embodiment of the invention, the sampler has two diode paths. Here the second diode path is provided for or effects compensation of temperature influences and/or an error voltage caused by the sampling current flow along the first diode path.
In still another embodiment of the invention, the potential control means are configured such that they permit the influence of at least one recessively discriminant signal level by influencing at least one threshold voltage in the receiver.
In another embodiment of the invention, the apparatus has (for the cooperative receiving means) means for specifying two threshold values. These means are referenced to a reference-earth potential busbar. In this case, the reference-earth potential busbar is operatively connected to a reference-earth potential terminal or can optionally be operatively connected to at least two alternative reference-earth potential terminals of the electronic module.
In accordance with a further embodiment of the present invention, an influence at the receiving-end is possible by means of an adjustable offset voltage source which lies in the supply current path, near to the reference-earth potential, of at least parts of the analog action of the receiving means.
In yet a further embodiment of the present invention, the reference-earth potential busbar of the threshold value specification means can be connected to the supply reference point, near to the reference-earth potential, at least of the parts of the analog action of the receiving means.
In still a further embodiment of the invention, the receiving means have level discrimination means referenced to a supply reference point. Here, this supply reference point is operatively connected to a reference-earth potential terminal or can (optionally) be operatively connected to at least two alternative reference-earth potential terminals of the electronic module.
In accordance with another embodiment of the invention, the apparatus comprises digital/analog conversion means and/or analog/digital conversion means.
In still another embodiment of the invention, the apparatus comprises digital/analog conversion means which can generate at least all the reference values, control and switching signals for potential influencing performed, where applicable, during the transmitting and/or receiving operation of the transceiver function.
In even another embodiment of the invention, in the apparatus, an offset voltage source that is referenced to a higher supply potential can also be replaced by a supply voltage source which is referenced to a lower supply potential and can correspondingly be varied in an offset manner.
In another embodiment of the invention, the apparatus is part of an electronic module which is designed and can be wired or driven for only single-wire reception and/or single-wire transmission (utilizing one line driver).
In another embodiment according to the present invention, the electronic module is an integrated semiconductor circuit.
In still another embodiment of the present invention, the apparatus is part of an integrated semiconductor circuit which carries, in addition to the apparatus, at least the means for providing the transceiver function for the microprocessor or microcontroller to the bus medium.
In accordance with another embodiment of the invention, the transceiver function, which cooperates with the apparatus, is designed for communication according to the CAN standard and for connection to a CAN bus line network (CAN_H/CAN_L).
In accordance with another embodiment of the invention, the transceiver function comprises receiving means having at least one input for the connection of at least one bus wire and an output for connection to the receive input of the microprocessor or microcontroller, and transmitting means having an input for connection to the transmit output of the microprocessor or microcontroller and at least one output for connection to at least one bus wire. Here, the transceiver function can be operated at least in the two different operating modes xe2x80x9ctransmit and receive/NORMALxe2x80x9d and xe2x80x9cno transmissionxe2x80x94only reception/RECEIVE ONLYxe2x80x9d and has an input port for the reception of a selection signal of the microprocessor or microcontroller for selection of one of these at least two operating modes.
In still another embodiment of the invention, the transceiver function comprises receiving means having two inputs for connection to the two bus wires and an output for connection to the receive input of the microprocessor or microcontroller, and transmitting means having an input for connection to the transmit output of the microprocessor or microcontroller and two outputs for connection to the two bus wires. The transceiver further comprises means which can set and/or reconfigure and/or adapt both the receiving means and the transmitting means to obtain the best possibility for emergency communication via the bus that still exists given the occurrence of a bus error which adversely affects normal communications via both bus wires. The transceiver further comprises bus error detection means and bus error evaluation means for conditioning at least one error or interrupt signal which can be output to the microcontroller, and also bus termination changeover means, which cooperate with the bus error detection means and can connect each of two termination elements. The two termination elements can be connected to two inputs of the transceiver function, to a bus wire assigned to it.
In another embodiment of the invention, the essential parts of the apparatus are arranged in a mobile test unit, which can be connected, on the one hand, to at least one bus wire and, on the other hand, to at least one terminating impedance in the electronic module and to the output of at least one transmission output stage of the transceiver function of the electronic module.
In even a further embodiment according to the invention, the apparatus comprises at least one changeover switch, by means of which the at least one output stage of the transmitting means of the electronic module can optionally be connected to the at least one bus wire or to at least one corresponding driving input of a backup means.
In accordance with another embodiment of the invention, the integrated semiconductor circuit carrying the apparatus is fabricated using high-voltage technology.
In yet another embodiment of the invention, the apparatus can be used for and (in this regard), is designed in or for one of the following: a transport means, a construction machine, a hoist, a control unit appertaining to automation technology, a control unit appertaining to electrical installation technology, a control unit appertaining to buildings technology, a control unit appertaining to heating technology, a control unit appertaining to air-conditioning technology, a control unit appertaining to alarm technology, a control unit appertaining to safety technology, a control unit appertaining to access control technology.
A number of exemplary embodiments are illustrated in the drawing and explained below. The method according to the invention and the apparatuses proposed according to the invention, and the elements of the said apparatuses, can be employed both in bus networks of single-wire operation and in bus networks of two-wire operation. When a two-wire bus network (following the CAN standard, for example) is used below in the drawing and description referring thereto, for the purpose of elucidation and functionality, this in no way represents a restriction of the invention to two-wire bus systems, but rather serves solely for avoiding text and repetition and thus for clarity.
In order to elucidate the method, firstly a few is simpler apparatuses will be explained which are expedient for xe2x80x9cone-at-a-timexe2x80x9d single-wire tests. Reference is made to the method in subsequent figures. Concluding figures illustrate further reaching apparatuses which are also suitable for xe2x80x9cone-at-a-timexe2x80x9d two-wire tests, permit a higher testing power and can readily be produced using semiconductor integration means, for example.